function setup() {

  createCanvas(600, 400);   

}

function draw() {

    background(250,175,40);

    fill(200,50,176);

    ellipse(x,50,50,50);

    x = x + speed;

        if(x + 25 >= width || x - 25 <= 0)

    {

        speed = -speed;

    }

}

​